1. Field of the Invention
The present invention relates to a starter for starting an engine.
2. Description of the Prior Art
FIG. 9 is a sectional view showing one example of a conventional starter disclosed in Japanese laid-Open Patent Application (Kokai) No. Hei 10-159692.
In FIG. 9, 1A is an output shaft. Coaxially arranged on this output shaft 1A are an electromagnet 2A, an overrunning clutch 30A provided with a pinion 30P adapted to engage with a ring gear 50A, a plunger 40A consisting of an inner plunger 4A and an outer plunger 4B, etc. A starter with this structure is generally called a coaxial type starter.
Reference numeral 12A is an armature of a DC motor and 16A is a shaft (a motor shaft). Numeral 18A is a deceleration mechanism for decelerating the torque of the shaft 16A and transmitting it to the output shaft 1A.
8A is a contact shaft which is supported by an internal gear member 17A of the deceleration mechanism 18A substantially parallel with the plunger 40A through a supporting hole 17m.
100 is a front bracket, 130 is a yoke, 400 is a rear bracket, and 800 is a shift plate which connects the outer plunger 4B to the contact shaft 8A.
The upper side from the central axis in FIG. 9 shows the state of a starter not in operation and the lower side from the central axis in FIG. 9 shows the state where the starter is in operation with an electromagnet turned ON and the pinion engages the ring gear.
In this starter, when an ignition switch is turned ON and an electric current flows to an exciting coil of the electromagnet 2A, the outer plunger 4B is attracted by an exciting core 2C of the electromagnet 2A. This conventional starter has such a structure that the outer plunger 4B is directly connected to the contact shaft 8A through the shift plate 800 and the contact shaft 8A also moves at the same time when the outer plunger 4B is attracted and moved by the exciting coil 2B. A coil spring 401 is disposed between the outer plunger 4B and the inner plunger 4A through a spring bearing member 401S. The inner plunger 4A is kept in the resting state because the coil spring 401 bends at the initial stage even when the outer plunger 4B starts the movement by attraction. Disposed in front of the inner plunger 4A through a shifter member 402 is an inner clutch 30B, which is also kept in the resting state while the inner plunger 4A is kept in the resting state. After a short interval when the outer plunger 4B starts the movement by attraction, a moving contact 80A mounted on the contact shaft 8A comes into contact with a stationary contact 80B disposed in a contact chamber ZA. When the moving contact 80A contacts with the stationary contact 80B, electric power is supplied from an external power source through a contact bolt 11A to start rotation of the armature 12A. When the output shaft 1A starts to turn through the deceleration mechanism 18A, the pinion 30P starts to move toward the ring gear 50A by the thrust generated in a helical spline portion 1B. Then, the crest and root of the pinion 30P agree and engage with those of the ring gear 50A. Thereafter, when the engine starts, the output shaft 1A is separated from the pinion 30P by the action of the overrunning clutch 30A and the pinion 30p runs idle. When the power supply to the exciting coil 2B is stopped, the pinion 30P is disengaged from the ring gear 50A by return springs 403, 404.
Further, the conventional electromagnet is assembled as shown in Japanese Laid-Open patent Application (Kokai) No. Hei 10-159692 etc. This is explained by taking the conventional starter as shown in FIG. 9 for instance. When the electromagnet 2A is mounted on the front bracket 100, a switch case 2k enclosing the exciting coil 2B is press-fitted direct or through another member such as rubber and resin to an electromagnet housing portion 110 of the front bracket 100.
As described above, the conventional electromagnet 2A of the starter is press-fitted to the electromagnet-housing portion 110 of the front bracket 1005 and assembled to control the radial movement, but since no axial control is provided, there is the possibility that the electromagnet 2A is caused to axially move by some vibration etc. and as a result, it gets out of the normal position (the switch-housing portion 110).
To prevent this problem, when the electromagnet 2A is mounted on the front bracket 100 according to a method as shown in FIGS. 10 and 11, the switch case 2K enclosing the exciting coil 2B is first inserted into the electromagnet housing portion 110. It is then fixed by crimping the open end G (the side of the deceleration mechanism 18A) of the front bracket 100 as shown by a mark F. According to this method, it is possible to prevent the electromagnet 2A from axially getting out of the normal position (the switch-housing portion 110) by crimping the open end G of the front bracket 100. However, in this case, there is added a process of crimping, and manufacturing costs are higher.
Also, when the inner components are assembled in the conventional starter as shown in FIG. 10, the overrunning switch 30A and a shaft section 1AK of the output shaft 1A on which the sliding surface (a helical spline) for the overrunning switch 30A is formed are first installed in the front bracket 100. Then, the electromagnet 2A is inserted into the switch-housing portion 110 of the front bracket 100 and secured in place by crimping. After this, it was necessary for a group of components pre-installing the plunger 4a, the deceleration mechanism 18A including a flange section 1AF of the output shaft 1A, and a contact chamber ZA including the contact shaft 8A to be assembled as a unit (The starter of FIG. 9 is also assembled in the same manner as this).
Namely, in this case, it is necessary to use the shaft section 1AK and the flange section which are separated in advance for the output shaft 1A (Namely, as shown in FIG. 6, once the output shaft integrally provided with a shaft section and a flange section is assembled first, it is impossible to coaxially mount the overrunning clutch 30A, the electromagnet 2A, the plunger 4a, etc. on the output shaft 1A).
In this case, when the output shaft 1A is formed by combining the shaft section 1AK with the flange section 2AF, press fitting or crimping is the only way to combine them each other. Since this causes the eccentricity of the shaft by deformation, it is difficult to secure the accuracy of squareness etc. of the shaft portion lAK and the flange portion 1AF. There is also a problem that the accuracy around the output shaft of the starter cannot be secured.